Who is Paul Ryan, Mitt Romney's running mate?

A fan of Ayn Rand, for starters.

Mitt Romney is to name Paul Ryan as his running mate on Saturday morning, according to Republican sources.

The vice-presidential candidate will be named at an event on the USS Wisconsin, in Virginia, but the campaign is yet to make an official announcement on the choice.

Ryan is a 42-year-old congressman from Wisconsin who was elected to the House of Representatives at 28. He is best know for his proposals for large spending and tax cuts - which increased his popularity with grassroots Republicans.

The New York Times political blog Five Thirty Eight named him as the "bold" choice of the two front runners (the other was Senator Rob Portman) - saying that Ryan was the "high risk, high reward" candidate:

Mr. Ryan would surely do more to excite the Republican base, and he could be a more dynamic figure on the campaign trail. But having never represented anything larger than a Congressional district, he is not as well vetted as Mr. Portman. Mr. Ryan, also, would introduce an ideological element to the campaign in the form of his conservative budget plan, which polls poorly with independent voters.

The blog suggested there were other places to look if Romney wanted to make a splash with the announcement, suggesting that, all considered, Ryan was just too risky. He was also dubbed the "long shot" for Romney's running mate in the New Yorker earlier this week, in an otherwise glowing review of his career as the Republican ideas man:

As in 2009, Republicans are divided between those who think they can win by pointing out Obama’s failures and those who want to run on a Ryan-like set of ideas. Romney seems to want to be in the first camp, but during the primaries he championed the ideas in Ryan’s budget. Ryan is frequently talked about as a future leader of the House Republicans and even as a long shot to be Romney’s running mate. He surely would take either job, but he seems better suited to continuing what he’s been doing since 2008: remaking the Republican Party in his image. You can’t “run on vague platitudes and generalities,” he told me earlier this month. He was speaking about Bush in 2004 and Obama four years ago. But he clearly believes that the same holds true for Romney in November.